Fix duplicate embedded callback hooks (#616)

Author: sjh9714

callbacks.go

@@ -3,6 +3,7 @@ package kong
 import (
 	"fmt"
 	"reflect"
+	"runtime"
 	"strings"
 )
 
@@ -127,13 +128,38 @@ func getMethod(value reflect.Value, name string) reflect.Value {
 	return method
 }
 
+func getExplicitMethod(value reflect.Value, name string) reflect.Value {
+	if isExplicitMethod(value.Type(), name) {
+		return value.MethodByName(name)
+	}
+	if value.CanAddr() && isExplicitMethod(value.Addr().Type(), name) {
+		return value.Addr().MethodByName(name)
+	}
+	return reflect.Value{}
+}
+
+func isExplicitMethod(t reflect.Type, name string) bool {
+	method, ok := t.MethodByName(name)
+	if !ok {
+		return false
+	}
+	// Promoted embedded methods are compiler-generated wrappers. The embedded
+	// value itself is visited separately, so skip those wrappers here.
+	fn := runtime.FuncForPC(method.Func.Pointer())
+	if fn == nil {
+		return true
+	}
+	file, _ := fn.FileLine(method.Func.Pointer())
+	return file != "<autogenerated>"
+}
+
 // getMethods gets all methods with the given name from the given value
 // and any embedded fields.
 //
 // Returns a slice of bound methods that can be called directly.
 func getMethods(value reflect.Value, name string) (methods []reflect.Value) {
 	walkEmbedded(value, func(v reflect.Value) {
-		if method := getMethod(v, name); method.IsValid() {
+		if method := getExplicitMethod(v, name); method.IsValid() {
 			methods = append(methods, method)
 		}
 	})

kong_test.go

@@ -2697,6 +2697,37 @@ func TestApplyCalledOnce(t *testing.T) {
 	assert.NoError(t, err)
 }
 
+type EmbeddedAfterApplyLeaf struct {
+	calls *int
+}
+
+func (l EmbeddedAfterApplyLeaf) AfterApply() error {
+	(*l.calls)++
+	return nil
+}
+
+type EmbeddedAfterApplyMiddle struct {
+	EmbeddedAfterApplyLeaf
+}
+
+type EmbeddedAfterApplyRoot struct {
+	EmbeddedAfterApplyMiddle
+}
+
+func TestPromotedEmbeddedAfterApplyCalledOnce(t *testing.T) {
+	calls := 0
+	cli := &EmbeddedAfterApplyRoot{
+		EmbeddedAfterApplyMiddle: EmbeddedAfterApplyMiddle{
+			EmbeddedAfterApplyLeaf: EmbeddedAfterApplyLeaf{
+				calls: &calls,
+			},
+		},
+	}
+	_, err := mustNew(t, cli).Parse(nil)
+	assert.NoError(t, err)
+	assert.Equal(t, 1, calls)
+}
+
 type envOnlyAfterApply struct {
 	called bool
 }